Preparation of Lepidocrocite and Maghemite by the Addition of Calcite to Iron(II) Chloride Solutions

Iron(III) oxyhydroxides such as goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) can be prepared via the oxidation of iron salts such as iron(II) chloride (FeCl2), iron(II) sulfate (FeSO4) and iron(III) nitrate [Fe(NO3)3] in solution based on adjusting the pH using sodium hydroxide (NaOH). Lepidocrocite can act as a precursor for the generation of maghemite (γ-Fe2O3), which exhibits unique magnetic, electrical and pharmacological properties and thus has attracted significant attention. The present study prepared lepidocrocite, goethite and the spinel structure iron oxides maghemite and magnetite (Fe3O4) without controlling the pH of the reaction solution. Specifically, both lepidocrocite and goethite were precipitated by oxidizing iron(II) chloride in solutions containing calcite (CaCO3) under air. The extent to which goethite was produced increased with increases in the calcite concentration. Spinel structure iron oxide particles with 50 nm in size were also obtained by oxidation of the same solutions under N2.